There is a large quantity of plastic ductwork and piping used in industry because of their beneficial corrosion resistance to a broad variety of aggressive chemicals. There is a large variety of plastic materials that are used for this purpose, including but not limited to polyvinyl chloride, polypropylene, polyethylene, and fiberglass reinforced plastics using a variety of thermoset resins.
Each of these presents its own challenges in terms of making field joints to connect the various section of ductwork and piping together in the field. Small diameter thermoplastic sections are generally assembled with the aid of adhesives; large diameter duct or pipe sections are generally assembled with the aid of permanent flanges made of the same materials which have been chemically welded to the duct or pipe sections. In fiberglass work, the conventional joint making mode is to use what is commonly known as "bell and spigot" joints. This is an industry term for the treatment of the ends of various sections of straight duct, fittings, or a combination of the two. One end, left as a trimmed raw edge the same size as the diameter of the duct or pipe, is the "small end or spigot end." The opposite end of the fitting or duct is enlarged, known as a bell, into which the spigot or small end fits.
In the thermoplastic field on small diameter sections a standard glue or resin may be used to coat the exterior of the spigot and/or the interior of the bell. This glue generally "melts" the materials so they bond very tightly together. The same type of joint may be used in fiberglass reinforced plastics; however, here, the bell and spigot are merely an aid to alignment in the field. In the case of the fiberglass materials, the duct and/or fitting close to the joint must first be sanded before the application of thermoset resin and glass fabric. The joint must be wrapped with various layers of glass saturated with resin in order to complete the joint. Once the resin hardens, the joint is set.
All of these non-metallic materials may be connected with flanges made of the basic virgin material from which the duct, pipe and/or fittings are made. For example, in the case of thermoplastics, and as an integral part of the duct or pipe, particularly on large diameters, a flange may be chemically welded to the ends of each duct, pipe and/or fitting, or may be made as an integral part of the duct or pipe, and these flanges are subsequently joined in the field. Such flanged joints require drilling of bolt holes, and the use of bolt sets and gaskets which connect flanged joints together in the field.
A similar operation may also occur with fiberglass reinforced plastics, both in ductwork and piping, where, at the ends of each section of duct and/or fitting, there may be an integrally bonded flange made of the fiberglass material. In other words, if a polyester or vinyl ester thermoset resin is used, the flange would be made out of the same resin and glass as the basic product. For example, SMACNA (Sheet Metal Air Conditioning Contractors National Association, Inc.) publishes manuals which deal with things such as PVC and fiberglass reinforced plastic ductwork. In these various manuals, specific recommendations are provided with respect to the thickness of the duct or flange, the sizes of the flange in relation to the duct or piping to which it is connected, the specific manner of making an integral bond between the duct or pipe and flange are shown, and specific dimensions are provided with respect to the size and location of the bolt holes around the bolt-hole circle where parts are to be joined.
All of these methods of making non-metallic field joint connections have deficiencies or certain dis-benefits which may make them undesirable in certain circumstances.
For many years, whether it be in marine services, petroleum services, pharmaceutical, waste water treatment, plating shops or semi-conductor services, etc., it has always been considered desirable to use flanged joints. The problem with flanged joints, however, is that the dimensions of flange face to flange face sections used in the field are very critical. It is common that buildings, as they are built, are subject to myriad changes so that one cannot apply pencil to paper in determining duct or pipe section lengths and expect to solve all problems. A large number of changes occur in the field before the building of a facility is completed which can place a duct or pipe system out of alignment and can cost millions of dollars to correct the problem.
Quite often, it would be preferred to use flanged joint sections without the inconvenience of costly, time consuming pre-determination of flange-face to flange-face dimensions for every single piece of material that goes into an industrial complex. It is also desirable to have a last-minute flexibility in this regard, and to be able to make adjustments in the field, so that any time that a flange/flange dimension might change, this change might be accommodated at the job-site quite readily after the changes of dimensions have occurred on a last-minute basis.
One of the largest single users of non-metallic material for ductwork and piping is the semiconductor industry. Non-metallic ductwork and piping are used for corrosion-resistant benefits. There are some unusual standards applied in the semiconductor industry, because of the manner in which the industry builds its buildings and systems. These semiconductor facilities use "clean rooms" to produce their chips. The interior finished areas are noted for their cleanliness and there is close control of any methods of construction or installations that may compromise super-clean environments. It is not uncommon for people to worry about dimensions of dirt particles such as 0.10 to 0.30 microns. A human hair in such an environment is considered an enormously large contaminant which could cause significant dollar losses.
In this atmosphere of such ultra-clean environments, there is also great concern about such things as odors, smoke or out-gassing of aggressive chemicals, which may destroy chips in the process of being made. Because of this, any activity that requires sawing, drilling, coating, painting, etc. is not desirable or permitted in some areas.
Thus, methods of fabrication and installations for "ordinary" services such as ductwork and piping become extremely complicated, because semiconductor or pharmaceutical industries absolutely will not tolerate what, not too many decades ago, was accepted as "common practice." Also, buildings are constructed on a "fast track", or accelerated schedule. It is not unusual for a $2 billion facility to be constructed and put in operation in 8 months. Such speed of construction reduces the financial burden on an owner, but it also creates problems where much construction must be done on the fly. There is great pressure to reduce time consumption on things like field joints for ductwork and piping.
It becomes desirable then, to create a means of joining ductwork and piping which does not require injurious odors from resins or adhesives, does not cause dust contamination by injurious sanding with resulting abrasive dust which must be cleaned up, or does not require the application of fiberglass materials which will spew forth particulate matter, nor the problems caused by dimensional tolerance mistakes, where parts may be a few inches too short or too long, and new replacement parts must be made at a remote factory. Such mistakes cause loss of time, which is loss of money. Being able to measure distances of points of connection in the field as the building is in fact being erected and thereafter being able to produce a flanged connection quickly, efficiently, and at low cost, is of great benefit, both in time and in reducing the burden of financing a project. Avoiding even one day's delay because of a goof might save an owner as much as a half-million dollars. Little things can be enormously costly. The solution to all these problems is the quick flange joint of this invention.